ASoC: msm: Fix to avoid crash during voip call

During voip call, size of downlink packet(frame.pktlen) is extracted
from userspace buffer. If size is greater than VOIP_MAX_VOC_PKT_SIZE
then it leads to crash due to unreferenced memory location. Fix to
make sure the size of downlink packet(frame.pktlen)value is less
than VOIP_MAX_VOC_PKT_SIZE.

Change-Id: Iaae62f3866150def35f13d9e05af0e28d81e51b4
Signed-off-by: Vidyakumar Athota <vathota@codeaurora.org>